have a 2.0hdi mk2 and the top up water level keeps flashing on even though there is enough water in tank, have changed the sensor and still the same problem, disconnected sensor and no warning, any advice would be greatly appreciated

Leave it disconnected, and keep an eye on your water level
Is it a new sensor, or 2nd hand ?
Check back on the wiring, in case there are any frayed edges, or bad connections ?
(Mine still does it occasionally, but I haven't got around to changing the sensor yet)

On my Xsara Picasso the light flashed on, on right hand high speed bends. When checked the water level was always correct. Eventually found it was the top of the radiator had separated and some fluid was leaking out, but not enough to show on header when stationary. Anyway I changed the rad and the fault never came back. This was a MK1 and supposedly the rad design was changed on later models. Easy to check look at header on rad, where it joins the fins of the core is there any sign of wet or blue green from antifreeze.

Go for a short drive see if it goes out then check radiator is getting hot below top pipe it could be similar fault to mine last posting 1.6 Hdi. However your model when I had a 2 litre one was a traditional Thermostat housing 3 bolts 120 degrees apart take it out and drop in boiling water in a pint Jug see if it is opening oK, Remember check all safety procedures on doing so re Hot Coolant and spillage on removing.The later models have a plastic housing slightly different hence my request for information

have a 2.0hdi mk2 and the top up water level keeps flashing on even though there is enough water in tank, have changed the sensor and still the same problem, disconnected sensor and no warning, any advice would be greatly appreciated

How long are you running the engine for before checking it is pressurised? It has to be hot to pressurise is the header tank cap sealing correctly? Some garages will pressurise the system with a pump to check for leaks.

How long are you running the engine for before checking it is pressurised? It has to be hot to pressurise is the header tank cap sealing correctly? Some garages will pressurise the system with a pump to check for leaks.

engine is running now and up to temp,

can tell it is pressurised as top hose cannot squeeze as easy when cold

On header tank there is a sensor for levels as shown in image provided turn anti-clockwise 90 degrees. (Engine Cold no pressure) A rubber 'O' ring seals the header tank when in situ so you will get a release of coolant when you pull the sensor out about 8 CM long. Deposits form over the 2 probes making a circuit inbetween hence faulty 1, 2, 3 bars etc 'Top Up Coolant' scrape these deposits off replace into header tank with cable at top seal ring pushed in then turn clockwise 90 degrees jobs a good one. Top up with coolant.

On header tank there is a sensor for levels as shown in image provided turn anti-clockwise 90 degrees. (Engine Cold no pressure) A rubber 'O' ring seals the header tank when in situ so you will get a release of coolant when you pull the sensor out about 8 CM long. Deposits form over the 2 probes making a circuit inbetween hence faulty 1, 2, 3 bars etc 'Top Up Coolant' scrape these deposits off replace into header tank with cable at top seal ring pushed in then turn clockwise 90 degrees jobs a good one. Top up with coolant.

done that already and also tried a brand new sensor, still the same fault